1. Field of the Invention
This invention relates to aqueous oral care compositions containing stannous compounds having increased stannous ion stability. In particular, this invention is directed to compositions containing stannous compounds stabilized with a combination of a water-soluble pyrophosphate salt and an organic acid compound. The compositions of the invention are particularly useful in the form of aqueous toothpaste, aqueous mouthwash and aqueous gel compositions exhibiting improved antitartar and antiplaque activity.
2. The Prior Art
There have been many proposals in the prior art to incorporate stannous compounds into oral health care products for the purpose of achieving particular clinical benefits such as caries prevention, plaque control and the reduction of gingivitis. Upon association with water or saliva, these stannous compounds release stannous ions which are active against oral bacteria and provide the desired benefits.
U.S. Pat. No. 3,956,479 discloses the use of quaternary anticalculus compounds in dental creams, containing polishing agents such as water-insoluble phosphates, binders, detergents, gelling agents, flavoring agents, and fluoride-containing compounds including stannous fluoride.
U.S. Pat. Nos. 3,711,604, 3,919,409, 3,935,306 and 3,980,767 disclose dentifrice formulations containing water soluble fluoride compounds, including stannous fluoride. The toothpaste formulations also include gelling agents such as carboxyvinyl polymers and insoluble abrasives such as silica and silicates.
U.S. Pat. No. 4,254,101 discloses compositions containing a humectant, silica abrasive, a carboxyvinyl polymer, water and fluoride compounds as optional ingredients. A variety of fluoride compounds including stannous fluoride are described as suitable optional ingredients. Phosphorus-containing anticalculus agents are also listed as optional ingredients.
U.S. Pat. No. 4,515,772 discloses oral compositions containing certain pyrophosphate salts as anticalculus formulations. A number of chelating agents are proposed as anticalculus agents, including ethylenediaminetetraacetic acid, nitrilotriacetic acid, polyphosphonates and carbonyl diphosphonates. An extensive list of fluoride ion sources is provided, including stannous fluoride.
U.S. Pat. No. 4,627,977 discloses dentifrice compositions containing a calculus-inhibiting amount of a linear molecularly dehydrated polyphosphate salt, and to inhibit hydrolysis of the polyphosphate salt in the saliva, a combination of a fluoride ion-providing source and a synthetic linear polymeric polycarboxylate. An extensive list of fluoride ion sources are provided, including stannous fluoride.
Formulations which contain stannous compounds such as stannous fluoride exhibit excellent clinical benefits, particularly in the reduction of gingivitis but have not been widely used in aqueous oral care formulations because of stability problems as the stannous ion is unstable and tends to react with other ingredients of the oral care composition to form insoluble inactive tin compounds, thereby reducing the effective amount of available stannous ion in the composition. Presently available commerical formulations contain SnF.sub.2 in anhydrous gels because of the instability of stannous ion in aqueous environments.
Numerous stannous compound oral care compositions with "stabilizing agents" have been proposed by the art.
U.S. Pat. No. 3,282,792 discloses the use of hydroxyl-substituted aliphatic di- and tri-carboxylic acids e.g. citric acid and malic acid as stabilizers for stannous fluoride in aqueous dentifrice compositions.
U.S. Pat. No. 3,445,567 discloses that aqueous stannous fluoride compositions can be stabilized with sorbitol or a mixture of sorbitol and glycerin.
U.S. Pat. No. 4,418,057 discloses a stannous fluoride oral care composition formulated as a non-aqueous gel mixture including anhydrous glycerin and an hydroxyethyl cellulose gelling agent. Total exclusion of moisture from the gel is required to protect the stannous ion.
U.S. Pat. No. 4,902,497 discloses dentifrices containing SnCl.sub.2 and gluconic acid.
U.S. Pat. No. 5,004,597 discloses an aqueous composition containing stannous fluoride wherein stannous chloride and stannous gluconate constitute a stannous reservoir to replace unstable stannous ion.
U.S. Pat. No. 5,017,363 discloses stannous fluoride toothpaste compositions containing an alkyl vinyl ether and maleic anhydride or acid copolymer as a stabilizing agent for stannous fluoride the composition being substantially free of soluble pyrophosphate salts, silica containing compounds and aldehyde group containing compounds.
U.S. Pat. Nos. 5,145,666 and 5,281,411 disclose a two component oral composition wherein one component contains stannous fluoride and stannous gluconate and the second component contains a pyrophosphate, the components being maintained separately before use.
U.S. Pat. No. 5,213,790 discloses a two component dentifrice wherein one component contains stannous fluoride and stannous gluconate and the other component contains a citrate ion source.
U.S. Pat. No. 5,281,410 discloses a two component oral composition wherein one component contains stannous fluoride and a stannous salt of an alpha hydroxy acid and a second component containing a pyrophosphate ion source.
U.S. Pat. No. 5,281,411 discloses dentifrices containing stannous gluconate and sodium monofluorophosphate and less than 0.05% stannous fluoride.
U.S. Pat. No. 5,258, 173 discloses the use of an antioxidant such as butylated hydroxy anisole in stannous fluoride dentifrices to reduce or prevent the conversion of stannous ions to stannic ions.